1. Field of the Invention
The present invention generally relates to a method for manufacturing a display device, and a substrate for the same. More particularly, the present invention relates to a method for manufacturing an active matrix liquid crystal display device (LCD) such as LCDs of TFT (Thin Film Transistor) type and MIM (Metal-Insulator-Metal) type, and a substrate used to manufacture the same.
2. Description of the Background Art
Recent improvement in performance of the display devices requires stricter management of the device characteristics. Management of the device characteristics is necessary for quality control, early detection of defective substrates, and prevention of outflow of such detective substrates into the process. For example, a TFT substrate of the LCD is fabricated by the process including a plurality of thin-film deposition steps and a plurality of patterning steps. In order to evaluate the manufacturing process and the like, characteristics such as TFT characteristics, bus line resistance and contact resistance are evaluated. One such evaluation method is to provide on a TFT substrate a TEG (Test Element Group) including test elements according to the purpose of evaluation, and measure characteristics of each test element by making a probe in contact with a terminal connected to that test element (for example, see Japanese Laid-Open Publication No. 8-190087, and in particular, FIGS. 1 and 2 thereof).
Since there exist various types of LCDs, kinds of characteristics to be evaluated and the number of such characteristics vary depending on the type of the LCD. In addition, kinds of test elements of the TEG and the number of such test elements also vary depending on the type of the LCD. For example, in the case of a TFT substrate having an organic insulation film entirely covering a picture element, characteristics associated with the organic insulation film are evaluated in addition to the characteristics that are evaluated for a TFT substrate having no organic insulation film. Moreover, since there are many sizes of the LCDs, the number of TEGs and their positions may be limited from the standpoint of the design. Recently, in order to manufacture many types of LCDs efficiently, the LCDs having different panel sizes are sometimes manufactured from the same mother substrate in the same production line. In other cases, the LCDs having different panel sizes are manufactured from the respective mother substrates having the same size. Since the position of the TEG and characteristics to be tested vary depending on the type of the LCD, separates probes are required for the respective types of the LCDs. In other words, expensive probes must be prepared in order to test the respective types of the LCD. Accordingly, a plurality of test apparatuses must be prepared for the respective types of the LCDs. Alternatively, when the same test apparatus is used, a probe must be replaced every time the type of the LCD is changed, complicating the manufacturing process. Moreover, the time to replace the probe is required, reducing the production efficiency.
In the recent display devices, the space for the TEG on the substrate has been increasingly reduced. The first reason for this is to reduce the production costs. In order to reduce the production costs, as many substrates as possible must be obtained from a single mother substrate. This requires the substrate area other than the display portion to be reduced as much as possible. Recently, the display devices tend to be specially developed for the medium- or small-size applications. Therefore, this is remarkable particularly in a small-size substrate for use in mobile products. The second reason is narrowing of the frame in the recent display devices. In order to narrow the frame portion (the portion other than the display portion) as much as possible, required terminals (such as drivers) and TEG must be formed in a narrow region. Accordingly, there is a need for development of a TEG efficiently integrating the test elements.
It is an object of the present invention to provide a display device substrate capable of being inexpensively evaluated with high operating efficiency, and thus achieving improved production efficiency. It is another object of the present invention to provide a method for manufacturing a display device with high production efficiency using a production line for manufacturing different types of display devices. In other words, it is another object of the present invention to efficiently manufacture various display devices in the same production line.
(1) According to the present invention, a method for manufacturing a display device using a production line for manufacturing at least two different types of display devices includes the steps of: fabricating a circuit substrate including a display device circuit of the display device and a plurality of test elements for evaluating characteristics of a circuit element forming the display device circuit; and evaluating the characteristics of the circuit element, the evaluating step including the step of measuring characteristics of the plurality of test elements formed on the circuit substrate, wherein each of the plurality of test elements is connected to at least one of a plurality of test terminals arranged with a common pattern in the at least two different types of display devices, and the measuring step is conducted with a common probe being in contact with the at least one test terminal regardless of the type of the display device.
Note that the phrase xe2x80x9cdifferent typesxe2x80x9d as used herein implies not only the difference in size of the display device and the difference in type of the circuit element forming the display device circuit but also the difference in manufacturing process of the circuit element, and the like. The term xe2x80x9ccircuit substratexe2x80x9d refers to a substrate having a plurality of circuit elements formed thereon, such as a TFT substrate and an MIM substrate (hereinafter, sometimes referred to as xe2x80x9cdisplay device substratexe2x80x9d). The term xe2x80x9ctest elementxe2x80x9d indicates an element formed in a free region on the substrate other than the region occupied by the display device circuit. The term xe2x80x9cdisplay device circuitxe2x80x9d indicates the overall circuitry required for operation as a display device, and includes not only picture-element electrodes in the display region, switch elements such as TFTs, wiring portions such as bus lines, and terminal portions, but also driving circuitry for driving the switch elements. The phrase xe2x80x9ca plurality of test terminals arranged with a common patternxe2x80x9d means that a plurality of test terminals provided in each of at least two different types of display devices are arranged with partially or completely the same pattern.
(2) In the manufacturing method according to (1), the circuit substrate includes a first test element group including at least two test elements for evaluating different characteristics from each other, the first test element group being connected to at least one of a plurality of first test terminals, and the plurality of first test terminals being included in the plurality of test terminals arranged with the common pattern.
(3) In the manufacturing method according to (2), the circuit substrate further includes a second test element group including at least two additional test elements for evaluating different characteristics from each other, the second test element group being connected to at least one of a plurality of second test terminals arranged with the same pattern as that of the plurality of first test terminals, and in the measuring step, the step of making the common probe in contact with the at least one of the plurality of first test terminals simultaneously is conducted independently of the step of making the common probe in contact with the at least one of the plurality of second test terminals simultaneously.
(4) In the manufacturing method according to (2), the at least two test elements include a resistance test element and a capacitance test element, the plurality of first test terminals are six first test terminals, the resistance test element is connected to four of the six first test terminals, and the capacitance test element is connected to the remaining two first test terminals of the six first test terminals.
(5) In the manufacturing method according to (4), the circuit substrate further includes a second test element group including at least two additional test elements for evaluating different characteristics from each other, the at least two additional test elements include an additional resistance test element and an additional capacitance test element, and the second test element group is connected to a plurality of second test terminals arranged with the same pattern as that of the plurality of first test terminals.
(6) In the measuring step of the manufacturing method according to (5), the step of making the common probe in contact with the plurality of first test terminals simultaneously is conducted independently of the step of making the common probe in contact with the plurality of second test terminals simultaneously.
(7) In the manufacturing method according to (1), the step of evaluating the characteristics of the circuit element includes the steps of specifying a type of the circuit substrate out of the at least two different types, obtaining information on measurement conditions according to the specified type and information on arrangement of the plurality of test terminals, and moving the common probe relative to the circuit substrate based on the obtained information on the measurement conditions and arrangement.
(8) In the manufacturing method according to (1), the step of fabricating the circuit substrate is a step of forming a plurality of circuit substrates on a mother substrate, and the step of evaluating the characteristics is sequentially conducted for the plurality of circuit substrates.
(9) In the manufacturing method according to (3), the first test element group and the second test element group include in common a test element for measuring the same characteristics, each of the test elements includes an element portion to be measured and a wiring portion for connecting the element portion to the test terminal, and the respective element portions of the test elements for measuring the same characteristics have different areas, the method further includes the step of: calculating a regression coefficient from respective measurement results of the test elements and the respective areas of the element portions.
A display device substrate according to the present invention includes: a display device circuit of a display device; and a plurality of test elements for evaluating characteristics of a circuit element forming the display device circuit, wherein the plurality of test elements include at least a first test element group and a second test element group each including a resistance test element and a capacitance test element that are arranged adjacent to each other, the first test element group is connected to at least one of a plurality of first test terminals arranged with a prescribed pattern, and the second test element group is connected to at least one of a plurality of second test terminals arranged with the same pattern as that of the plurality of first test terminals.
In the display device substrate of the present invention, the plurality of first test terminals are six first test terminals, the resistance test element is connected to four of the six first test terminals, and the capacitance test element is connected to the remaining two first test terminals of the six first test terminals.
The xe2x80x9cdisplay device substratexe2x80x9d of the present invention is a substrate having a size adaptable to an intended display device, and is typically fabricated by cutting a mother substrate having a plurality of display device substrates formed thereon into a prescribed size.
According to the present invention, a measuring system for measuring characteristics of the plurality of test elements included in the display device substrate of the present invention includes: a probe including a plurality of contact portions arranged with the same pattern as that of the plurality of first test terminals on the display device substrate; a means for reading information attached to a cassette that contains a plurality of mother substrates each having a plurality of display device substrates formed thereon; a means for taking a mother substrate out of the cassette based on the information read by the reading means; a first determination means for determining whether or not there is any test element on the mother substrate, which has not been measured; a means for moving the probe relative to the test element on the display device substrate according to a type of the mother substrate, when the first determination means determines that there is a test element that has not been measured; a means for making the plurality of contact portions of the probe in contact with a plurality of test terminals including the terminal connected to the test element, and measuring characteristics of the test element; a second determination means for determining whether or not the cassette contains any mother substrate that has not been measured, when the first determination means determines that there is not any test element that has not been measured; a means for taking the mother substrate that has not been measured out of the cassette, when the second determination means determines that the cassette contains a mother substrate that has not been measured; a third determination means for determining whether there is any cassette that has not been measured, when the second determination means determines that the cassette does not contain any mother substrate that has not been measured; and a means for moving the cassette that has not been measured so as to allow the reading means to read the information, when the third determination means determines that there is a cassette that has not been measured.
Hereinafter, effects of the present invention will be described. In the method for manufacturing a display device according to the present invention, each of a plurality of test elements for evaluating characteristics of a circuit element forming a display device circuit is connected to at least one of a plurality of test terminals arranged with a common pattern in at least two different types of display devices. Moreover, characteristics of the plurality of test elements are measured with a common probe being in contact with the at least one test terminal regardless of the type of the display device. According to this manufacturing method, characteristics of the circuit element can be evaluated with the common probe regardless of the type of the display device. This eliminates the need to prepare a probe for every type of display device and to replace the probe according to the type of display device. Therefore, characteristics of the circuit element can be inexpensively evaluated with high operating efficiency, whereby the display device can be manufactured efficiently.
In the manufacturing method according to (2), the circuit substrate includes a first test element group including at least two test elements for evaluating different characteristics from each other. According to this manufacturing method, at least two different characteristics included in the first test element group can be evaluated with the common probe.
In the manufacturing method according to (3), the circuit substrate further includes a second test element group including at least two additional test elements for evaluating different characteristics from each other. The second test element group is connected to at least one of a plurality of second test terminals arranged with the same pattern as that of the plurality of first test terminals. In the measuring step, the step of making the common probe in contact with the at least one of the plurality of first test terminals simultaneously is conducted independently of the step of making the common probe in contact with the at least one of the plurality of second test terminals simultaneously. According to this manufacturing method, respective characteristics of the first test element group and the second test element group can be measured using the common probe. This eliminates the need to replace the probe for measurement of the respective characteristics of the first test element group and the second test element group. Thus, characteristics of the circuit element can be inexpensively evaluated with high operating efficiency, whereby the display device can be manufactured efficiently. Moreover, according to this manufacturing method, the probe is made in contact with the at least one of the test terminals simultaneously. Therefore, by using a set of at least two test elements included in each of the first test element group and the second test element group, i.e., a set of at least two test elements for evaluating different characteristics from each other, characteristics of at least two test elements can be measured with one probe contact operation for each test element group.
In the manufacturing method according to (4), the first test element group includes a resistance element and a capacitance test element, allowing for efficient evaluation of the characteristics of the circuit element. In particular, for a substrate such as a TFT substrate and an MIM substrate, not only the resistance but also the capacitance must be measured. Therefore, the first test element group including the resistance test element and the capacitance test element enables efficient measurement of the resistance and capacitance.
Moreover, in the manufacturing method according to (4), the resistance test element is connected to four of the six first test terminals, and the capacitance test element is connected to the remaining two first test terminals of the six first test terminals. According to this manufacturing method, the resistance test element is connected to four first test terminals. Therefore, resistance measurement accuracy is improved by a four-terminal method. Even when the resistance test element is replaced with a TFT test element, connecting the TFT test element to three of the four first test terminals enables measurement of characteristics of the TFT test element.
Six first test terminals are provided because the following advantages are obtained: first, connecting the resistance test element to the four first test terminals enables accurate measurement of metal sheet resistance. In other words, the metal sheet resistance can be measured by the four-terminal measurement method, enabling more accurate measurement of the sheet resistance than measurement using two terminals.
Second, the contact portions of the probe contacting the four test terminals connected to the resistance test element (hereinafter, sometimes referred to as resistance measuring terminals) can be provided separately from the contact portions of the probe contacting the two test terminals connected to the capacitance test element (hereinafter, sometimes referred to as capacitance measuring terminals). Therefore, the measuring apparatus can be prevented from being complicated, and reduction in measurement accuracy can be prevented. For example, if a probe having four contact portions contacting resistance measuring terminals are also used as a probe contacting two capacitance measuring terminals, switching between resistance measurement and capacitance measurement is required, complicating the measurement apparatus and also possibly reducing the measurement accuracy due to insertion of a switching device. In view of the increasing needs for fine display devices, reduction in measurement accuracy is highly problematic. Accordingly, it is desirable to use a probe having six separate contact portions, that is, four contact portions contacting the resistance measuring terminal and two contact portions contacting the capacitance measuring terminal. It is therefore desirable to provide six first test terminals contacting the probe.
Third, the four contact portions of the probe contacting the four resistance measuring terminals can also be used as contact portions for measuring the TFT test element. Since the TFT test element is connected to three test terminals, a probe having at least three contact portions is required in order to measure the TFT characteristics. For example, in the case where the TFT characteristics and the capacitance are measured using a probe having four contact portions, at least one contact portion must be used for measuring both the TFT characteristics and the capacitance. Therefore, switching between measurement of the TFT characteristics and capacitance measurement is required. On the other hand, in the case where the TFT characteristics and the capacitance are measured without switching between measurement of the TFT characteristics and capacitance measurement, a probe having five contact portions may be used. However, when the resistance and the capacitance are measured using this probe, only three contact portions can be assigned to resistance measurement. Therefore, the resistance cannot be measured by the four-terminal measurement method. Accordingly, in order to measure the resistance, capacitance and TFT characteristics accurately without switching, a probe having at least six contact portions is required, and therefore at least six test terminals contacting the contact portions of this probe are required.
It can be appreciated from the above advantages that six first test terminals, that is, combination of four resistance measuring terminals and two capacitance measuring terminals, are the minimum unit for improving measurement accuracy without complicating the measuring apparatus.
In the manufacturing method according to (5), the circuit substrate further includes a second test element group including at least two additional test elements for evaluating different characteristics from each other, and the at least two additional test elements include an additional resistance test element and an additional capacitance test element. The second test element group is connected to a plurality of second test terminals arranged with the same pattern as that of the plurality of first test terminals. According to this manufacturing method, at least two different characteristics, i.e., resistance and capacitance, can be evaluated for each of the first test element group and the second test element group by using the common probe in the manufacturing method according to (4).
Providing the minimum unit of test terminals, that is, combination of four test terminals connected to a resistance test element and two test terminals connected to a capacitance test element, enables characteristics to be evaluated in a versatile manner regardless of the type and size of the display device. For example, in the case of a small display device, the minimum required number of test element groups are configured from a resistance test element and a capacitance test element. Moreover, the minimum unit of test terminals, that is, six test terminals, is connected to both test elements included in each test element group. Since both test elements included in each test element group form the minimum test unit connected to the minimum unit of test terminals, the test element group can be formed even in a small region on the substrate without being subjected to positional limitations. In the case of a large display device, the use of an increased number of test element groups enables more detailed evaluation of the characteristics.
In the measuring step of the manufacturing method according to (6), the step of making the common probe in contact with the plurality of first test terminals simultaneously is conducted independently of the step of making the common probe in contact with the plurality of second test terminals simultaneously. According to this manufacturing method, the probe is made in contact with the at least one of the test terminals simultaneously. Therefore, by using a set of a resistance test element and a capacitance test element included in each of the first test element group and the second test element group, characteristics of the resistance test element and the capacitance test element can be measured with one probe contact operation for each test element group.
In the manufacturing method according to (7), the step of evaluating the characteristics of the circuit element includes the steps of specifying a type of the circuit substrate out of the at least two different types, obtaining information on measurement conditions according to the specified type and information on arrangement of the plurality of test terminals, and moving the common probe relative to the circuit substrate based on the obtained information on the measurement conditions and arrangement. According to this manufacturing method, characteristics of the circuit element can be successively evaluated for different type of circuit substrates by using the common probe.
In the manufacturing method according to (8), the step of fabricating the circuit substrate is a step of forming a plurality of circuit substrates on a mother substrate, and the step of evaluating the characteristics is sequentially conducted for the plurality of circuit substrates. According to this manufacturing method, the step of evaluating the characteristics can be sequentially conducted for the plurality of circuit substrates formed on the mother substrate by using the common probe.
In the manufacturing method according to (9), the first test element group and the second test element group include in common a test element for measuring the same characteristics. Each of the test elements includes an element portion to be measured and a wiring portion for connecting the element portion to the test terminal. The element portions of the test elements included in common in the first test element group and the second test element group have different areas between the first test element group and the second test element group. A regression coefficient is calculated from the measurement results of the respective test elements in the first test element group and the second test element group and the areas of the respective element portions in the first test element group and the second test element group. According to this manufacturing method, characteristics of the test elements included in common in different test element groups can be evaluated more accurately based on the measurement results of these test elements and the areas of the respective element portions of the test elements.
In the display device substrate of the present invention, the plurality of test elements include at least a first test element group and a second test element group each including a resistance test element and a capacitance test element that are arranged adjacent to each other. The first test element group is connected to at least one of a plurality of first test terminals arranged with a prescribed pattern, and the second test element group is connected to at least one of a plurality of second test terminals arranged with the same pattern as that of the plurality of first test terminals. According to this display device substrate, the resistance test element and the capacitance test element included in each of the first test element group and the second test element group are arranged adjacent to each other. Therefore, the resistance test element and the capacitance test element can be efficiently formed on the circuit substrate in view of the space on the substrate or the preference of characteristics to be evaluated. Moreover, the first test terminals and the second test terminals are arranged with the same pattern. Therefore, characteristics of the resistance test element and the capacitance test element included in each of the first test element group and the second test element group can be measured with the common probe.
In the display device substrate, the resistance test element is connected to four of the six first test terminals, and the capacitance test element is connected to the remaining two first test terminals of the six first test terminals. According to this display device substrate, the resistance test element is connected to four first test terminals. Therefore, resistance measurement accuracy is improved by a four-terminal method. Even when the resistance test element is replaced with a TFT test element, connecting the TFT test element to three of the four first test terminals enables measurement of characteristics of the TFT test element.
Providing the minimum unit of test terminals, that is, combination of four test terminals connected to a resistance test element and two test terminals connected to a capacitance test element, enables characteristics to be evaluated in a versatile manner regardless of the type and size of the display device. For example, in the case of a small display device, the minimum required number of test element groups are configured from a resistance test element and a capacitance test element. Moreover, the minimum unit of test terminals, that is, six test terminals, is connected to both test elements included in each test element group. Since both test elements included in each test element group form the minimum test unit connected to the minimum unit of test terminals, the test element group can be formed even in a small region on the substrate without being subjected to positional limitations. In the case of a large display device, the use of an increased number of test element groups enables more detailed evaluation of the characteristics.
The measuring system according to the present invention is a system for measuring characteristics of the plurality of test elements included in the display device substrate of the present invention, allowing for successive measurement using the common probe. This enables automated measurement rather than manual measurement, resulting in improved production efficiency.